c2 magnús t. guðmundsson
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Geothermal activity within the subglacial Katlacaldera, Iceland
Magnús T. Gudmundsson, Þórdís Högnadóttir, Hannah I. Reynolds, Eyjólfur Magnússon
Nordvulk, Institute of Earth Sciences, University of Iceland
GEORG Workshop 25 November 2016
Katla caldera• the second largest caldera in Iceland• 100 km2 and up to 700 m deep• Filled with 400-700 m of ice• One of the most dangerous volcanoes in
Iceland• Geothermal activity in many parts of
caldera
From Larsen (2000)
Kjartan Guðmundsson 1918Katla volcano: • Renown for eruptions and • associated jökuhlaups (glacier
outburst floods) • 21 known eruptions since 9th
century AD• Last such event in 1918• Everybody has been waiting since
about 1960 for the next one
Geothermal activity:ice cauldrons formed by basal melting
Two types:• Accumulation of meltwater and
sudden, discrete drainage events• Continuous drainage
Both types observed in Katla
Geophysical signals 1:
Seismic undershooting –shallow magma chamber
(Ólafur Gudmundsson et al., 1994)
Geophysical signals 2:
Aeromagnetic surveyingnon-magnetic body in centreof caldera
(Jónsson and Kristjánsson, 2000)
Geophysical signals 3:
Bouguer anomaly mapping:Large intrusion under caldera –relatively low-density body at shallow depth encircled by highdensity bodies
(Gudmundsson, 1994, Larsen et al., 2013)
Geothermal activity and structure:• Geothermal activity within
caldera• Aligned along caldera rim• Over and near inner margins of
shallow high density bodies• No geothermal activity directly
above the shallow, seismicallyimaged, magma body
Based on:Ó. Gudmundsson et al. 1994Jónsson and Kristjánsson, 2000Larsen et al. 2013Gudmundsson et al., 2007
Events in 9 July 2011: Sudden flood – drainage of ice cauldrons - bridge destroyed
Chemical analysis of floodwater and cauldron development suggestincreased geothermal activity
9 July 2011
Events in 9 July 2011: Sudden flood – drainage of ice cauldrons - bridge destroyed
Chemical analysis of floodwater and cauldron development suggestincreased geothermal activity
9 July 2011
11 July 2011
Summary:
• Large caldera – geothermal activity correlates withcaldera faults
• Ice cover conceals geothermal areas• Monitoring of cauldrons allows approximate power
estimates• Possible to monitor variations in power• Variations of time scale 1-4 years observed 1999-
2016• Peaks in geothermal activity correlated with other
activity (seismicity, uplift, flooding)
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